This invention relates to power supply apparatus and, more particularly, to apparatus having minimal power dissapation for supplying an output voltage of substantially constant range regardless of the range of variation of an input voltage.
In general, power supplies are known wherein an input AC line voltage is used to derive an output voltage of constant magnitude. Typically, the output voltage is a regulated DC voltage having minimal ripple factor and exhibiting a substantially constant magnitude held within a constrained range of variations.
Heretofore, such power supplies have been designed to account, or compensate, for very large variations in the amplitude of the AC input line voltage. However, it has been found that, to account for this large range of voltage variation, an undesirable amount of power dissipation must be provided. For example, if the input AC line voltage increases so as to greatly exceed an optimum value, the regulated output voltage produced by the power supply must not similarly increase. Nevertheless, the excess input voltage must somehow be dissipated. Usually, this is provided with conventional power dissipating elements, with the result that excessive heat often is produced and, moreover, an unnecessary amount of power is supplied to the power supply. This, of course, requires that the various circuit elements exhibit suitably high operating power levels; and, moreover, the higher the cost of operating the powered apparatus at such higher power levels is not preferable.
These prior power supplies are further complicated by the fact that they must be designed with the anticipation that the input voltage levels also are susceptible to significant reduction. Hence, suitable amplification must be provided to ensure that the regulated voltage produced by these power supplies is, nevertheless, maintained during such power reductions.
Therefore, it is apparent that there has been a long felt need for a power supply which can satisfactorily operate throughout a wide range of input voltage levels while enabling a substantially constant regulated voltage to be derived therefrom. Moreover, there has been a clear need for such power supplies wherein only a minimum amount of unnecessary power is dissipated.
It is apparent that such power supplies having minimum power dissipation can be used to energize various appliances, signal processing apparatus, and virtually any other electrical device. Moreover, such power supplies which are capable of providing the same output voltage regardless of the amplitude and range of variations in the amplitude of an input voltage can advantageously be used even in those locations wherein the precise line voltage is not known. As an example, a user of a device wherein such a power supply is incorporated can readily power that device directly from the input AC voltage in both the United States wherein the line voltage is approximately 110 volts and in Europe where the line voltage is approximately 220 volts. A desirable feature of this power supply is that no manual switching or other operation is necessary to account or compensate for such differences in the input AC line voltage.